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United States Patent |
6,069,221
|
Chasser
,   et al.
|
May 30, 2000
|
Powder coating compositions containing a carboxylic acid functional
polyester
Abstract
Disclosed are improved curable powder coating compositions comprised of a
particulate, film-forming mixture of a polymer having reactive functional
groups, and a curing agent therefor having functional groups reactive with
the functional groups of the polymer and present in an amount sufficient
to cure the coating composition, wherein the inclusion of a particular
polyester which has carboxylic acid functional groups improves adhesion to
metal, particularly aluminum, and filiform corrosion resistance.
Inventors:
|
Chasser; Anthony M. (Allison Park, PA);
Schneider; John R. (Glenshaw, PA);
Singer; Debra L. (Wexford, PA)
|
Assignee:
|
PPG Industries Ohio, Inc. (Cleveland, OH)
|
Appl. No.:
|
127193 |
Filed:
|
July 31, 1998 |
Current U.S. Class: |
528/26 |
Intern'l Class: |
C08G 077/04 |
Field of Search: |
528/26
|
References Cited
U.S. Patent Documents
4091049 | May., 1978 | Labana et al. | 428/417.
|
4681811 | Jul., 1987 | Simpson et al. | 428/413.
|
4703101 | Oct., 1987 | Singer et al. | 528/87.
|
4937288 | Jun., 1990 | Pettit, Jr. et al. | 525/176.
|
4988767 | Jan., 1991 | Pettit, Jr. | 525/194.
|
5407707 | Apr., 1995 | Simeone et al. | 427/410.
|
5543464 | Aug., 1996 | Decker et al. | 525/176.
|
Other References
Filiform Corrosion in Polymer-coated Metals, A. Bautista, Progress in
Organic Coatings 28, pp. 49-58 (1996).
|
Primary Examiner: Boykin; Terressa M.
Attorney, Agent or Firm: Uhl; William J.
Parent Case Text
This is a Continuation-in-Part of copending application Ser. No.
08/995,790, filed on Dec. 22, 1997, which is a Continuation-in-Part of
copending application Serial No. 08/904,597, filed Aug. 1, 1997.
Claims
What is claimed is:
1. In a curable powder coating composition comprising a particulate
film-forming mixture of a polymer containing reactive functional groups
and a curing agent therefor having functional groups reactive with the
functional groups of the polymer and being present in an amount sufficient
to cure said polymer, the improvement comprising the inclusion in said
composition of a polyester having carboxylic acid functional groups, said
polyester comprising an oligomer having the following structure:
##STR2##
and where the polyester is present in an amount ranging from 2 to 5 weight
percent based on total weight of resin solids in the powder coating
composition, said amount being sufficient to improve the adhesion to metal
and filiform corrosion resistance of the powder coating composition, but
insufficient to cure the coating composition in the absence of the curing
agent.
2. In a curable powder coating composition comprising a particulate
film-forming mixture of a polymer containing reactive functional groups
and a curing agent therefor having functional groups reactive with the
functional groups of the polymer and being present in an amount sufficient
to cure said polymer, the improvement comprising the inclusion in said
composition of a polyester having carboxylic acid functional groups, said
polyester being the reaction product of the following reactants:
(a) pentaerithrytol; and
(b) a dicarboxylic acid having the following structure:
HOOC--R--COOH
wherein R is C.sub.7 to C.sub.10 alkylene or a six-membered cyclic alkylene
group, and where the polyester is present in an amount ranging from 2 to 5
weight percent based on total weight or resin solids in the powder coating
composition, said amount being sufficient to improve the adhesion to metal
and filiform corrosion resistance of the powder coating composition, but
insufficient to cure the coating composition in the absence of the curing
agent.
3. The powder coating composition of claim 2 wherein when R is C.sub.10
alkylene.
4. The powder coating composition of claim 2 wherein when R is a
six-membered cyclic alkylene group.
5. The powder coating composition of claim 1 wherein the polymer containing
reactive functional groups is selected from the group consisting of a
polyester polymer having carboxylic acid functional groups and an acrylic
polymer having carboxylic acid functional groups.
6. The powder coating composition of claim 5 wherein the curing agent is a
beta-hydroxyalkylamide.
7. The powder coating composition of claim 5 wherein the curing agent is
triglycidylisocyanurate.
8. The powder coating composition of claim 5 wherein the curing agent is a
polyepoxide.
9. The powder coating composition of claim 1 wherein the polymer containing
reactive functional groups is an acrylic polymer having epoxy functional
groups.
10. The powder coating composition of claim 9 wherein the curing agent is a
polycarboxylic acid different from said polyester.
11. A coated article comprising an aluminum substrate and a cured coating
thereon, said cured coating being derived from a curable powder coating
composition comprising a particulate film-forming mixture of a polymer
containing reactive functional groups and a curing agent therefor having
functional groups reactive with the functional groups of the polymer and
being present in an amount sufficient to cure said polymer, wherein the
improvement comprises the inclusion in said composition of a polyester
comprising an oligomer having the following structure:
##STR3##
and where the polyester is present in an amount ranging from 2 to 5 weight
percent based on total weight of resin solids in the powder coating
composition, said amount being sufficient to improve the adhesion to metal
and filiform corrosion resistance of the powder coating composition, but
insufficient to cure the coating composition in the absence of the curing
agent.
12. A coated article comprising an aluminum substrate and a cured coating
thereon, said cured coating being derived from a curable powder coating
composition comprising a particulate film-forming mixture of a polymer
containing reactive functional groups and a curing agent therefor having
functional groups reactive with the functional groups of the polymer and
being present in an amount sufficient to cure said polymer, wherein the
improvement comprises the inclusion in said composition of a polyester
having carboxylic acid functional groups, said polyester being the
reaction product of the following reactants:
(a) pentaerithrytol; and
(b) a dicarboxylic acid having the following structure:
HOOC--R--COOH
wherein R is C.sub.7 to C.sub.10 alkylene or a six-membered cyclic alkylene
group, and where the polyester is present in an amount ranging from 2 to 5
weight percent based on total weight of resin solids in the powder coating
composition, said amount being sufficient to improve the adhesion and
filiform corrosion resistance of the powder coating composition, but
insufficient to cure the coating composition in the absence of the curing
agent.
13. The coated article of claim 12 wherein when R is C.sub.10 alkylene.
14. The coated article of claim 12 wherein when R is a six-member cyclic
alkylene group.
15. The coated article of claim 12 wherein the polymer containing reactive
functional groups is selected from the group consisting of a polyester
polymer having carboxylic acid functional groups and an acrylic polymer
having carboxylic acid functional groups.
16. The coated article of claim 15 wherein the curing agent is a
beta-hydroxyalkylamide.
17. The coated article of claim 15 wherein the curing agent is
triglycidylisocyanurate.
18. The coated article of claim 15 wherein the curing agent is a
polyepoxide.
19. The coated article of claim 13 wherein the polymer containing reactive
functional groups is an acrylic polymer having epoxy functional groups.
20. The coated article of claim 19 wherein the curing agent is a
polycarboxylic acid different from said polyester.
Description
BACKGROUND OF THE INVENTION
The present invention relates to powder coating compositions with improved
adhesion and filiform corrosion resistance.
More specifically, the invention relates to a powder coating composition
comprising a solid particulate film-forming mixture of a polymer
containing reactive functional groups and a curing agent therefor having
functional groups reactive with the functional groups of the polymer with
an additive to improve adhesion and filiform corrosion resistance.
Powder coating compositions for use in painting are extremely desirable.
Such coating compositions can eliminate the organic solvents used in
liquid paints. When the powder coating composition is thermally cured,
little, if any, volatile material is given off to the surrounding
environment. This is a significant advantage over liquid paints in which
organic solvent is volatilized into the surrounding atmosphere when the
paint is cured by heating.
A particular problem which often results from the use of powder coatings,
particularly over aluminum substrates, is filiform corrosion. Filiform
corrosion generally occurs in wet environments at the site of a surface
defect in the presence of soluble ionic species. As described in Filiform
Corrosion in Polymer-coated Metals, A. Bautista, PROGRESS IN ORGANIC
COATINGS 28 at pages 49-58 (1996), this deterioration process gives rise
to corrosion products which are characterized by a filamentous, worm-like
appearance under the coatings. The "filaments" typically exhibit an
arborescent structure and grow directionally under the coating.
Filiform corrosion can result in delamination of the coating from a metal
substrate and it has become a matter for increasing concern in the areas
of automotive, industrial and architectural coatings. Accordingly, it is
desirable to provide a powder coating composition with improved filiform
corrosion. It has been found that incorporation of certain polyesters
having multiple carboxylic acid functional groups improves the filiform
corrosion resistance of the powder coating composition.
Pending U.S. patent application Ser. No. 08/995,790 filed Dec. 22, 1997
discloses a powder coating composition having improved filiform corrosion
resistance, wherein the improvement is due to the inclusion in the
composition of an organic polysiloxane having various pendant reactive
functional groups. Examples of these pendant functional groups include
COOH, NCO, carbamate, primary and secondary amine and epoxy functional
groups.
U.S. Pat. No. 5,543,464 teaches a powder coating composition comprised of
an epoxy functional group containing acrylic polymer, and, as curing
agents, a crystalline polycarboxylic acid and a semi-crystalline
polycarboxylic acid group containing polyester. The polycarboxylic acid
group containing polyesters are based on a polycondensation reaction of
(cyclo) aliphatic and/or aromatic polyols with (cyclo) aliphatic and/or
aromatic polycarboxylic acids or anhydrides, esters or acid chlorides
based on these acids. These acid functional polyester curing agents impart
enhanced flexibility and improved impact resistance to the resultant
coating.
U.S. Pat. No. 4,937,288 discloses a thermosetting powder coating
composition which comprises a co-reactable particulate mixture of a
carboxylic acid group-containing acrylic polymer, a second carboxylic acid
group-containing material with crystallinity sufficient to assist the flow
of the composition as it cures, and a beta-hydroxyalkylamide curing agent.
The second carboxylic acid group-containing material is selected from the
class of C.sub.4 to C.sub.20 aliphatic dicarboxylic acids, polymeric
polyanhydrides, and preferably, low molecular weight carboxylic acid
group-containing polyesters. The second carboxylic acid group-containing
material provides flexibility and impact resistance of the resultant
coating, as well as assisting in flow during cure of the powder coating
composition.
U.S. Pat. No. 5,407,707 discloses a powder coating composition which
comprises a solid, particulate mixture of 60 to 90 percent by weight of an
epoxy functional copolymer and 10 to 40 weight percent of a polycarboxylic
acid crosslinking agent. Suitable polycarboxylic acid crosslinking agents
include crystalline aliphatic materials such as adipic, succinic, sebacic,
azelaic and dodecanedioic acid. Low molecular weight polycarboxylic acid
group-containing polyesters and half-acid esters can also be used.
SUMMARY OF THE INVENTION
The curable powder coating composition of the present invention comprises a
particulate film-forming mixture of a polymer containing reactive
functional groups and a curing agent therefor having functional groups
reactive with the functional groups of the polymer and being present in an
amount sufficient to cure the composition, the improvement comprising the
inclusion in the composition of a polyester having multiple carboxylic
acid functional groups, said polyester comprising an oligomer having the
following structure:
##STR1##
wherein n is 2 to 4, and
R is C.sub.7 to C.sub.10 alkylene or a six-membered cyclic alkylene group,
and where the polyester is present in an amount sufficient to improve the
adhesion to metal and filiform corrosion resistance of the powder coating
composition, but insufficient to cure the coating composition in the
absence of the curing agent.
The polyester is the reaction product of pentaerithrytol and an excess of a
dicarboxylic acid which has the following general structure:
HOOC--R--COOH (II)
wherein R is C.sub.10 alkylene or a six-membered cyclic alkylene group.
The coating compositions of the invention are particularly useful for
coating aluminum substrates.
DETAILED DESCRIPTION OF THE INVENTION
As aforementioned, the polyester can be prepared by a polycondensation
reaction of pentaerithrytol and an excess of a dicarboxylic acid having
the formula (II), wherein R is C.sub.7 to C .sub.10 alkylene or a
six-membered cyclic alkylene group.
Preferably, when R is C .sub.10 alkylene, the polyester is the reaction
product of pentaerithrytol and dodecanedioic acid. When R is a
six-membered cyclic alkylene group, the polyester is preferably the
reaction product of pentaerithrytol and 1,4-cyclohexane dicarboxylic acid.
The pentaerithrytol and the dicarboxylic acid are reacted together at a
molar ratio of from 1:6 to 1:8, preferably at a ratio of 1:8. A large
excess of acid is desired to ensure an adduct with acid functionality
having a number average molecular weight (M.sub.n, as determined by gel
permeation chromatography using a polystyrene standard) in the range of
from 1000 to 4000, preferably from 2000 to 3000 The resultant low
molecular weight polyester has an acid number of 310 to 420 (i.e., an acid
equivalent weight of 130 to 180) and is a semi-crystalline solid at room
temperature. Further, the resultant polyester having carboxylic acid
functionality has a melting range of from 115.degree. C. to 130.degree.
C., preferably from 118 .degree. C. to 123.degree. C. By
"semi-crystalline" is meant exhibiting a heterogeneous morphology, i.e.,
crystalline and amorphous phases; and typically opaque at ambient
temperatures.
It should be appreciated that the above-described polycondensation reaction
results in a complex mixture of monomers, i.e., unreacted pentaerithrytol
and dicarboxylic acid; polyester oligomer and polyester polymer, which
contains the polyester oligomer depicted in structure (I) above.
Besides the dicarboxylic acid, lower alkyl esters of the dicarboxylic acids
can be used, such as C.sub.1 ro 4 alkyl esters. Also, anhydride of the
dicarboxylic acids, where they exist, can be used. Therefore, the term
dicarboxylic acid is meant to include the acid itself and its functional
equivalents, the lower alkyl esters and the anhydrides.
The polyester having carboxylic acid functional groups is typically present
in the powder coating compositions in an amount sufficient to improve the
adhesion to metal and filiform corrosion resistance of the powder coating
composition, but insufficient to cure the coating composition in the
absence of a curing agent. Typically, the polyester is present in an
amount ranging from 1 to 30 weight percent, preferably from 2 to 10 weight
percent, and more preferably from 2 to 5 weight percent, based on the
total weight of resin solids in the powder coating composition. It is, of
course, understood that the polyester is different from the polymers
containing reactive functional groups and curing agents which are
described below.
Polymers Containing Reactive Functional Groups
The polymer containing reactive functional groups suitable for use in the
powder coating compositions of the invention can be chosen from a variety
of materials, including, for example, acrylic polymers, polyurethane
polymers, or polyester polymers having carboxylic acid functional groups,
or acrylic polymers having epoxy functional groups.
In a preferred embodiment of the invention, the polymer containing reactive
functional groups is a carboxylic acid group-containing acrylic polymer.
Such polymers can be formed by reacting a polymerizable alpha,
beta-ethylenically unsaturated carboxylic acid with one or more
polymerizable, unsaturated monomers. Examples of carboxylic acid
group-containing monomers which can be used are acrylic acid and
methacrylic acid, which are preferred, as well as crotonic acid, itaconic
acid, fumaric acid, maleic acid, citraconic acid and the like, and
monoalkylesters of unsaturated dicarboxylic acids.
Examples of other suitable monomers include vinyl aromatic compounds such
as styrene, alkyl-substituted styrenes such as alpha-methylstyrene and
halide-substituted styrene such as chlorostyrene. Other suitable
polymerizable, ethylenically unsaturated monomers which can be used are
esters of acrylic and methacrylic acid such as methacrylate, ethyl
acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate,
ethyl methacrylate, N-butyl methacrylate, and 2-ethylhexyl methacrylate.
In addition to the aforementioned ethylenically unsaturated,
copolymerizable monomers, nitriles, such as acrylonitrile, vinyl and
vinylidene halides such as vinyl chloride and vinylidene fluoride, and
vinyl esters such as vinyl acetate may be used.
The carboxylic acid group containing acrylic polymers are typically
prepared under conventional free radical initiated polymerization
conditions such as those described in U.S. Pat. No. 4,988,767 at column 3,
line 58 to column 4, line 8, incorporated herein by reference. The
carboxylic acid group-containing acrylic polymers can also be prepared by
other techniques well known in the art such as emulsion polymerization,
suspension polymerization, bulk polymerization or suitable combinations
thereof.
The polymer containing reactive functional groups can also be a carboxylic
acid group-containing polyurethane polymer. Such polymers can be prepared
by reacting polyols and polyisocyanates so as to form a polyurethane
polyol which is then reacted with polycarboxylic acid or anhydride to
introduce free carboxyl groups into the reaction product. Examples of
suitable polyols include aliphatic polyols such as ethylene glycol,
propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol,
cyclohexanedimethanol, trimethylolpropane and the like. Examples of
suitable polyisocyanates are aromatic and aliphatic polyisocyanates with
the aliphatic polyisocyanates being preferred for exterior durability.
Specific examples include 1,6-hexamethylene diisocyanate, isophorone
diisocyanate and 4,4'-methylene-bis-(cyclohexyl isocyanate). Examples of
suitable polycarboxylic acids and anhydrides include succinic acid, adipic
acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid,
tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid and
anhydrides of such acids.
In another preferred embodiment of the invention, the polymer containing
reactive groups is a carboxylic acid group-containing polyester polymer.
Such polyester polymers which are useful are those based on a condensation
reaction of aliphatic polyols, including cycloaliphatic polyols, with
aliphatic and/or aromatic polycarboxylic acids and anhydrides. Examples of
suitable aliphatic polyols include 1,2-ethanediol, 1,3-propanediol,
1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexane dimethanol,
trimethylol propane, and the like. Suitable polycarboxylic acids and
anhydrides include those as are described above in connection with the
preparation of the carboxylic acid group-containing polyurethane. The
polyol and the acid or anhydride are reacted together with an excess of
acid over alcohol so as to form a polyester which has free carboxylic acid
groups.
In another preferred embodiment, the polymer containing reactive functional
groups is an epoxy functional group-containing acrylic polymer. Such epoxy
functional group-containing acrylic polymers are typically copolymers of
an ethylenically unsaturated monomer having at least one epoxy group and
at least one polymerizable, ethylenically unsaturated monomer which is
free of epoxy groups.
Examples of ethylenically unsaturated monomers containing epoxy groups are
those containing 1,2-epoxy groups and include glycidyl acrylate, glycidyl
methacrylate and allyl glycidyl ether.
Examples of ethylenically unsaturated monomers which do not contain epoxy
groups are alkyl esters of acrylic and methacrylic acid containing form 1
to 20 carbon atoms in the alkyl group. Specific examples include methyl
methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate,
butyl acrylate, and 2-ethylhexyl acrylate.
Suitable other copolymerizable ethylenically unsaturated monomers include
vinyl aromatic compounds such as styrene, and vinyl toluene; nitriles such
as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such
as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl
acetate. Acid group-containing copolymerizable ethylenically unsaturated
monomers such as acrylic acid and methacrylic acid are preferably not used
because of the possible reactivity of the epoxy and acid groups.
The epoxy functional group-containing acrylic polymer is typically prepared
by conventional means which are well known in the art, such as those
described in U.S. Pat. No. 4,703,101 at column 2, lines 29 to 44,
incorporated herein by reference.
The various materials used to form the functional group containing polymers
of the present invention are selected such that the resultant material has
a high glass transition temperature (T.sub.g), that is, greater than
30.degree. C. The T.sub.g, which is a measure of the hardness and melt
flow of a polymer, can be calculated as described by Fox in Bull. Amer.
Physics. Soc., 1,3 page 123 (1956). The T.sub.g can also be measured
experimentally and differential scanning calorimetry can be used (rate of
heating 10.degree. C. per minute, T.sub.g taken at the first inflection
point). Unless otherwise indicated, the stated T.sub.g as used herein
refers to the calculated T.sub.g in the case of acrylic polymers, and
measured T.sub.g in the case of condensation polymers such as polyesters
and polyurethanes.
Typically, the polymer containing reactive functional groups is present in
the powder coating composition of the invention in an amount ranging from
20 to 97 weight percent, preferably from 50 to 85 weight percent, said
weight percentages based on the total weight of resin solids in the powder
coating composition.
Curing Agents
As described above, the powder coating composition of the invention also
comprises a curing agent having functional groups reactive with the
functional groups of the polymer.
Polyepoxides as curing agents for carboxylic acid group-containing polymers
are well known in the art. Examples of polyepoxides suitable for use as
curing agents in the powder coating compositions of the present invention
are those described in U.S. Pat. No. 4,681,811 at column 5, lines 33 to
58, incorporated herein by reference.
Beta-hydroxyalkylamides as curing agents for carboxylic acid
group-containing polymers are well known in the art. Examples of
beta-hydroxyalkylamides suitable for use as curing agents in the powder
coating compositions of the invention are those described in U.S. Pat. No.
4,801,680 at column 2, line 42 to column 3, line 9, incorporated herein by
reference.
Also useful as a curing agent for carboxylic acid group-containing
polymers, as is well known in the art, is triglycidylisocyanurate (TGIC),
a weatherable epoxy crosslinker commercially available as ARALDITE TM
PT-810 from Ciba-Geigy.
Polyacids, particularly polycarboxylic acids, as curing agents for epoxy
functional group-containing acrylic polymers are well known in the art.
Examples of polycarboxylic acids and polycarboxylic acid group-containing
polyesters suitable for use as curing agents in the powder coating
compositions of the invention are those described in U.S. Pat. No.
5,407,707 at column 3, line 55 to column 4, line 10, incorporated herein
by reference.
It is essential that the curing agent having functional groups reactive
with the functional groups of the polymer is present in an amount
sufficient to cure the powder coating composition. Typically, the curing
agent is present in the powder coating composition of the invention in an
amount ranging from 2 to 50 weight percent, preferably from 5 to 20 weight
percent, said weight percentages based on the total weight of resin solids
in the powder coating composition.
The powder coating compositions of the present invention can optionally
include other materials such as pigments, fillers, light stabilizers,
anti-oxidants and flow control agents and anti-popping agents.
A pigment can be included in the coating in amounts of up to 60 per cent by
weight based on total weight of the composition in order to give a
suitable color to the resultant coating. Suitable pigments include, for
example, titanium dioxide, ultramarine blue, phthalocyanine blue,
phthalocyanine green, carbon black, graphite fibrils, black iron oxide,
chromium green oxide, ferride yellow and quindo red.
In addition, the powder coating composition may include fumed silica or the
like to reduce caking of the powder during storage. An example of a fumed
silica is commercially available from Cabot Corporation under the
trademark CAB-O-SIL. The fumed silica is present in amounts ranging up to
1 percent by weight based on total weight of the powder coating
formulations.
For good exterior durability, the compositions also can contain ultraviolet
light absorbing agents, ultraviolet light stabilizers and antioxidants.
Such materials are commercially available from Ciba-Geigy under the
trademarks TINUVIN and IRGANOX. The ultraviolet light absorbing agents,
ultraviolet light stabilizers and antioxidants, when used, are typically
present in the compositions individually in amounts up to 6 percent by
weight based on weight of resin solids.
One group of suitable flow control agents are acrylic polymers such as
polylauryl acrylate, polybutyl acrylate, poly(2-ethylhexyl) acrylate,
poly(ethyl-2-ethylhexyl) acrylate, polylauryl methacrylate and
polyisodecenyl methacrylate. The flow control agent may also be a
fluorinated polymer such as an ester of polyethylene glycol or
polypropylene glycol and fluorinated fatty acids, for example, an ester of
polyethylene glycol of a molecular weight of over 2,500 and
perfluorooctanoic acid. Polymeric siloxanes of molecular weights over
1,000 may also be used as a flow control agent, for example,
poly(dimethylsiloxane) or poly(methylphenyl)siloxane. The flow control
agent, when used, is present in amounts up to 5 percent by weight based on
total weight of the coating composition.
Anti-popping agents can be added to the composition to allow any volatile
material to escape from the film during baking. Benzoin is a preferred
anti-popping agent and when used is generally present in amounts up to 3.0
percent by weight based on total weight of the powder coating composition.
The powder coating compositions are typically prepared by melt blending the
ingredients. This can be accomplished by first blending the ingredients in
a high shear mixer such as a planetary mixer, and then melt blending in an
extruder from 80.degree. C. to 130.degree. C. The extrudate is then cooled
and pulverized into a particulate material which can be applied by
spraying.
The particulate powder coating compositions can be applied directly to a
substrate of, for example, metal such as steel or aluminum, or to a primed
metal substrate. In particular, when the particulate coating compositions
of the invention are applied to unprimed aluminum substrates as clear
coats, an improvement in adhesion and filiform corrosion resistance is
noted. Application can be by spraying, and in the case of a metal
substrate, by electrostatic spraying which is preferred, or by the use of
a fluidized bed. The coating composition can be applied as a primer or as
a primer surfacer, or as a topcoat or as a finishing coat. The powder
coating can be applied in a single sweep or in several passes to provide a
film having a thickness after cure of from 1 to 10 mils (25.4 to 254
microns), usually 2.0 to 4.0 mils (50.8 to 100.4 microns).
After application of the powder coating composition, the powder coated
substrate is baked at a temperature sufficient to cure the product,
typically at 250.degree. F. to 400.degree. F. (121.degree. to 204.degree.
C.) for 1 to 60 minutes, and preferably at 300.degree. F. to 350.degree.
F. (160.degree. to 175.degree. C.) for 15 to 30 minutes.
The following examples illustrate the invention and should not be construed
as a limitation on the scope thereof. Unless specifically indicated
otherwise, all percentages and amounts are by weight.
EXAMPLES
Examples 1 through 5 describe the preparation of various carboxylic acid
functional polyesters. Example 1 describes the preparation of a carboxylic
acid functional polyester based on pentaerithrytol and dodecanedioic acid.
Example 2 describes the preparation of a carboxylic acid functional
polyester based on pentaenthrytol and 1,4-cyclohexane dicarboxylic acid
and Example 3 describes the preparation of a carboxylic acid functional
polyester based on 1,6-hexanediol and dodecanedioic acid. Examples 5 and 6
describe the preparation of polyesters based on pentaerithrytol and adipic
acid, and di-trimethylol propane and adipic acid, respectively.
Examples A through D describe the preparation of various powder
compositions. Example A describes the preparation of two powder coating
compositions based on a carboxylic acid functional acrylic polymer and a
polyepoxide curing agent. Example A-1 describes a powder coating
composition containing the carboxylic acid functional polyester of Example
1 for improved filiform corrosion resistance, while Comparative Example
A-2 contains no polyester.
Example B describes the preparation of six powder coating compositions
based on an epoxy functional group containing acrylic polymer and a
carboxylic acid group containing curing agent. Each of the Examples B-1
through B-5 contains a carboxylic functional polyester of Example 1
through Example 5, respectively. Comparative Example B-6 contains no
polyester.
Example C describes the preparation of four powder coating compositions
based on a carboxylic acid functional polyester polymer and a
beta-hydroxyalkylamide curing agent. Each of Examples C-1 through C-3
incorporates a polyester of Example 1 through Example 3, respectively.
Comparative Example C-4 contains not carboxylic acid functional polyester.
Example D describes the preparation of two powder coating compositions
based on an epoxy functional group containing acrylic polymer and a
carboxylic acid functional materials. Example D-1 contains both the
carboxylic acid functional polyester of Example 1 and a carboxylic acid
functional curing agent, while Comparative Example D-2 contains only the
carboxylic acid functional polyester with no curing agent.
Example 1
This example describes the preparation of a carboxylic acid functional
polyester based on pentaerithrytol and dodecanedioic acid. The polyester
is prepared from a mixture of the following ingredients:
______________________________________
Parts by Weight Equivalent
Ingredients: (grams) % on Solids Weight
______________________________________
Pentaerithrytol
544.64 6.88% 34.04
Dodecanedioic acid 7360.00 92.92% 115.00
Dibutyl tin oxide 7.90 0.10% --
Triphenyl phosphite 7.90 0.10% --
Total 7920.45 100%
______________________________________
The above ingredients were combined in a suitable reaction vessel equipped
with a thermocouple, stirrer, nitrogen gas inlet and a partial condenser
with a distilling head. Under a light nitrogen sparge, the reaction
mixture was heated to a temperature of 151.degree. C. over a period of 3.5
hours, whereupon water began to distill off. Heating was continued as the
temperature increased to 180.degree. C. over a one hour period. That
temperature was held over a period of 3.5 hours to a stalled acid value of
about 352. At this time approximately 218.0 grams of water had been
collected.
The polyester thus prepared was a fluid liquid which upon discharge from
the reaction flask, was permitted to cool, yielding a semi-crystalline
solid with an acid value of 351.5.
Example 2
This example describes the preparation of a carboxylic acid functional
polyester based on pentaerithrytol and 1,4-cyclohexane dicarboxylic acid.
The polyester is prepared from a mixture of the following ingredients:
______________________________________
Parts by Weight Equivalent
Ingredients: (grams) % on Solids Weight
______________________________________
Pentaerithrytol
204.24 8.98% 34.04
Cyclohexanediacid 2066.16 90.82% 86.09
Dibutyl tin oxide 2.27 0.10% --
Triphenyl phosphite 2.27 0.10% --
Total 2274.94 100%
______________________________________
The above ingredients were combined in a suitable reaction vessel equipped
with a thermocouple, stirrer, nitrogen gas inlet and a partial condenser
with a distilling head. Under a light nitrogen sparge, the reaction
mixture was heated to a temperature of about 158.degree. C. over a period
of about 2.5 hours, whereupon water began to distill off. Heating was
continued as the temperature increased to about 200.degree. C. over a 0.75
hour period. That temperature was held over a period of about 0.5 hour to
a stalled acid value of about 466. At this time approximately 83.0 grams
of water had been collected.
The polyester thus prepared was a fluid liquid which upon discharge from
the reaction flask, was permitted to cool, yielding a semi-crystalline
solid with an acid value of 462.9.
Example 3
This example describes the preparation of a carboxylic acid functional
polyester based on 1,6-hexanediol and dodecanedioic acid. The polyester is
prepared from a mixture of the following ingredients:
______________________________________
Parts by Weight Equivalent
Ingredients: (grams) % on Solids Weight
______________________________________
1,6-Hexanediol
826.00 29.28% 59.00
Dodecanedioic acid 1993.18 70.67% 115.00
Dibutyl tin oxide 1.41 0.05% --
Total 2820.59 100%
______________________________________
The above ingredients were combined in a suitable reaction vessel equipped
with a thermocouple, stirrer, nitrogen gas inlet and a partial condenser
with a distilling head. Under a light nitrogen sparge, the reaction
mixture was heated to a temperature of about 151.degree. C. over a period
of about 2 hours, whereupon water began to distill off. Heating was
continued as the temperature increased to about 220.degree. C. over about
a 3.5 hour period. That temperature was held over a period of about 1.5
hours to a stalled acid value of about 72.8. At this time approximately
215 grams of water had been collected.
The polyester thus prepared was a fluid liquid which upon discharge from
the reaction flask, was permitted to cool, yielding a semi-crystalline
solid with an acid value of 76.2.
Example 4
This example describes the preparation of a carboxylic acid functional
polyester based on pentaerithrytol and adipic acid. The polyester is
prepared from a mixture of the following ingredients:
______________________________________
Parts by Weight Equivalent
Ingredients: (grams) % on Solids Weight
______________________________________
Pentaerithrytol
204.24 10.42% 34.04
Adipic acid 1752.00 89.38% 73.00
Dibutyl tin oxide 1.96 0.10% --
Triphenyl phosphite 1.96 0.10% --
Total 1960.15 100%
______________________________________
The above ingredients were combined in a suitable reaction vessel equipped
with a thermocouple, stirrer, nitrogen gas inlet and a partial condenser
with a distilling head. Under a light nitrogen sparge, the reaction
mixture was heated to a temperature of about 156.degree. C. over a period
of about 2.0 hours, whereupon water began to distill off. Heating was
continued as the temperature increased to about 200.degree. C. over a 1.0
hour period. That temperature was held over a period of about 0.5 hour to
a stalled acid value of about 545.2. At this time approximately 83.0 grams
of water had been collected.
The polyester thus prepared was a fluid liquid which upon discharge from
the reaction flask, was permitted to cool, yielding a semi-crystalline
solid with an acid value of 537.5.
Example 5
This example describes the preparation of a carboxylic acid functional
polyester for use as an additive in the powder coating compositions of the
invention. The polyester is prepared from a mixture of the following
ingredients:
______________________________________
Parts by Weight Equivalent
Ingredients: (grams) % on Solids Weight
______________________________________
Di-trimethylol propane
190.17 17.80% 63.39
Adipic acid 876.00 82.00% 73.00
Dibutyl tin oxide 1.07 0.10% --
Triphenyl phosphite 1.07 0.10% --
Total 1068.30 100%
______________________________________
The above ingredients were combined in a suitable reaction vessel equipped
with a thermocouple, stirrer, nitrogen gas inlet and a partial condenser
with a distilling head. Under a light nitrogen sparge, the reaction
mixture was heated to a temperature of about 157 C. over a period of about
1.5 hours, whereupon water began to distill off. Heating was continued as
the temperature increased to about 180.degree. C. over a 1.25 hour period.
That temperature was held over a one hour period to a stalled acid value
of about 497.8. At this time approximately 34.0 grams of water had been
collected.
The polyester thus prepared was a fluid liquid which upon discharge from
the reaction flask, was permitted to cool, yielding a semi-crystalline
solid with an acid value of 497.3.
Powder Coating Composition
Testing Procedures
Each of the following powder coating compositions was electrostatically
applied to cleaned only aluminum substrate (commercially available from
ACT, Inc. as A407A1), then cured as described below. The powder coated
panels were then tested for various physical properties to include solvent
resistance/extent of cure, 20.degree. gloss, filiform corrosion resistance
and general appearance. The powder coating formulations were tested for
stability and thermal shock resistance.
Solvent resistance/extent of cure was tested according to ASTM D5402 using
methyl ethyl ketone (MEK) double rubs. Results are reported for appearance
and mar after 200 double rubs, or, alternately, as the number of double
rubs completed before breaking through the coating to the substrate.
20.degree. gloss was determined using a BYK-Gardner haze-glossmeter.
Appearance was evaluated via visual inspection.
Filiform corrosion resistance was tested by scribing the cured coated
substrate, exposing the scribed test panel in the Copper Accelerated
Acetic Acid Salt Spray ("CASS") test cabinet according to ASTM B368-68 for
6 hours, then thoroughly rinsing the panel with deionized water. These
rinsed panels were subsequently exposed to an 85% relative
humidity/60.degree. C. environment for a period of up to 4 weeks. Results
reported represent the average length (in millimeters) of corrosion
filiments as measured outward from the scribe line.
Powder stability was tested by placing a sealed 2 ounce sample of the
powder coating composition in a water bath at 40.degree. C. for one week.
The powder was then examined for caking and/or fusing together of powder
particles. Thermal shock resistance was tested by soaking cured powder
coated panels in water at 100.degree. F. for 4 hours, then immediately
transferring the panels to a 30.degree. C bath to cool. Once cooled,
panels were scribed and within 30 seconds the scribed area was exposed to
a 5 psi steam blast. Panels were then visually examined for blushing,
water spotting and adhesion loss. Results are reported as pass/fail.
Example A
This example describes the preparation of two powder coating compositions
based on a carboxylic acid functional acrylic polymer and a polyepoxide
curing agent. Example A-1 contains the carboxylic acid functional
polyester for improved filiform corrosion resistance, and Comparative
Example A-2 contains no polyester. Each of the examples was prepared from
a mixture of the following ingredients:
______________________________________
Example A-1
Comparative Example A-2
Ingredients: (grams) (grams)
______________________________________
TGIC.sup.1 67.8 41.6
CRYLCOAT 450.sup.2 357.0 432.5
Pentasiloxane.sup.3 30.4 30.3
Polyester of Example 1 50.8 --
URAFLOW B.sup.4 5.2 5.2
IRGANOX 1076.sup.5 5.1 5.1
RESIFLOW PL-200.sup.6 5.6 5.6
TROY 570.sup.7 5.2 5.2
______________________________________
.sup.1 Triglycidylisocyanurate, commercially available from CYTEC Corp.
.sup.2 Acid functional polyester, commercially available from UCB
Chemicals..
.sup.3 Acid functional polysiloxane (SiO).sub.5, the preparation of which
is described in Example 2 of U.S. patent application Ser. No. 08/995,790,
filed 22 December 1977.
.sup.4 Benzoin, commercially available from Monsanto Chemical Co.
.sup.5 Polyphenol antioxidant available from CibaGeigy Corp.
.sup.6 Silica/acrylic polymer dispersion, a flow control additive
available from Estron Chemical, Inc.
.sup.7 Silicone/amide flow control additive, available from Troy Chemical
Corp.
The ingredients of each of the Examples A-1 and A-2 immediately above were
mixed via typical powder compounding techniques. Each powder composition
was electrostatically applied to cleaned only aluminum substrate then
cured at 340.degree. F. (171.degree. C.) for 20 minutes, and tested as
described above for filiform corrosion resistance, haze rating, haze
cracking and 20.degree. gloss. The following Table 1 illustrates the
advantages for improved filiform corrosion resistance, while maintaining
other performance properties, obtained by the incorporation of the
carboxylic acid functional polyester into the powder coating composition.
TABLE 1
______________________________________
Example A-2
Test performed: Example A-1 (Comparative)
______________________________________
20.degree. Gloss
89 88
Thermal shock Pass Fail
Filiform corrosion 5 mm, medium density 8 mm, high density
______________________________________
Example B
This example describes the preparation of six powder coating compositions
based on an epoxy functional group containing acrylic polymer and a
carboxylic acid group containing curing agent. Each of the Examples B-1
through B-5 contains a carboxylic acid functional polyester of Example 1
through Example 5, respectively. Comparative Example B-6 contains no
polyester. Each of the examples was prepared from a mixture of the
following ingredients:
______________________________________
Exam- Exam- Exam- Exam- Exam- Example
ple ple ple ple ple B-6
B-1 B-2 B-3 B-4 B-5 com-
Ingredients: (grams) (grams) (grams) (grams) (grams) parative
______________________________________
Polyester of
65.6 -- -- -- -- --
Example 1
Polyester of -- 65.6 -- -- -- --
Example 2
Polyester of -- -- 65.6 -- -- --
Example 3
Polyester of -- -- -- 65.6 -- --
Example 4
Polyester of -- -- -- -- 65.6 --
Example 5
Dode- 95.7 108.6 63.8 117.2 112.5 65.6
canedioic
acid
GMA acrylic 384.8 371.8 416.7 363.4 367.9 414.8
resin.sup.1
EPON 23.0 23.0 23.0 23.0 23.0 23.0
1001F.sup.2
URAFLOW 2.9 2.9 2.9 2.9 2.9 2.9
B
TINUVIN 2.4 2.4 2.4 2.4 2.4 2.4
900.sup.3
TROY 570 2.4 2.4 2.4 2.4 2.4 2.4
______________________________________
.sup.1 ALMATEX A207S available from Reichold Chemicals, Inc.
.sup.2 Polyglycidyl ether of Bisphenol A, having an equivalent weight of
1000, available from Shell Oil and Chemical Co.
.sup.3 Micronized
2(2hydroxy-benzotriazol-2-yl)-4,6-bis(methyl-1-phenylethyl)phenol, an
ultraviolet absorber light stabilizer available from CibaGeigy Corp.
The ingredients of each of the Examples B-1 through B-6 immediately above
were mixed via typical powder compounding techniques. Each powder
composition was electrostatically applied to cleaned only aluminum
substrate then cured at 340.degree. F. (171.degree. C.) for 20 minutes,
and tested as described above for filiform corrosion resistance, haze
rating, stability, thermal shock and 20.degree. gloss. The following Table
2 illustrates the advantages of improved filiform corrosion resistance,
while maintaining other performance properties, obtained by the
incorporation of the particular carboxylic acid functional polyesters of
Example 1 and Example 2 into the powder coating composition.
TABLE 2
______________________________________
Exam- Exam- Exam- Exam- Exam- Exam-
Test ple ple ple ple ple ple
Performed: B-1 B-2 B-3 B-4 B-5 B-6
______________________________________
Appearance
Clear; Exu- Clear;
Heavy Powder
Clear;
sharp date; sharp exudate too sharp
dull un-
stable*
Stability 7 days, 7 days, 7 days, 7 days, -- 7 days,
@35.degree. C. good good slight cake good
cake
Thermal pass, fail, pass fail, -- pass
shock slight chip slight
haze chip,
haze
Filiform 2 mm., 5 mm., 5.5 0 mm., -- 9 mm.,
corrosion low low mm., heavy high
density density low exudate density
density
______________________________________
*It should be noted that the carboxylic acid functional polyester of
Example 5 was very soft, hence the powder coating composition which
incorporated this material was unstable. As a result, no data was
generated for powder coating composition of Example B5.
Example C
This example describes the preparation of four powder coating compositions
based on a carboxylic acid functional polyester polymer and a
beta-hydroxyalkylamide curing agent. Each of the Examples C-1, C-2 and C-3
incorporates a carboxylic acid functional polyester (different from the
aforementioned carboxylic acid functional polymer), and Comparative
Example C-4 contains no carboxylic acid functional polyester. The powder
coating compositions were prepared from a mixture of the following
ingredients:
______________________________________
Example Example Example
Example C-4
C-1 C-2 C-3 (comparative)
Ingredients: (grams) (grams) (grams) (grams)
______________________________________
Polyester of
31.3 -- -- --
Example 1
Polyester of -- 31.3 -- --
Example 2
Polyester of -- -- 31.3 --
Example 3
PRIMID AL-552.sup.1 40.9 45.8 28.7 26.9
DSM-P800.sup.2 453.1 448.1 465.0 498.1
URAFLOW B 2.0 2.0 2.0 2.0
MICROWAX C.sup.3 4.5 4.5 4.5 4.5
TINUVIN 900 11.0 11.3 11.3 11.3
TINUVIN 144.sup.4 5.7 5.7 5.7 5.7
TROY 570 5.7 5.7 5.7 5.7
HCA-1.sup.5 5.7 5.7 5.7 5.7
Total 560 554 554 560
______________________________________
.sup.1 Betahydroxyalkylamide curing agent, available from EMSAmerican
Grilon, Inc.
.sup.2 Ultradurable acid functional polyester available from DSM Resins.
.sup.3 Wax C MicroPowder, a fatty acid amide (bisstearamide of ethylene
diamine) available from HoechstCelanese.
.sup.4
2tert-butyl-2-(4-hydroxy-3,5-di-tert-butylbenzyl)[bis(methyl2,26,6-tetram
thyl-4-piperinyl)dipropionate, an ultraviolet light stabilizer available
from CibaGeigy Corp.
.sup.5 9,10dihydro-9-oxa-10-phosphaphenanthene-10-oxide (or
3,4,5,6dibenzo-1,2-oxaphosphane-2-oxide), an antiyellowing agent availabl
from Sanko Chemical Co., Ltd.
The ingredients of each of the Examples C-1 through C-4 immediately above
were mixed via typical powder compounding techniques. Each powder
composition was electrostatically applied to cleaned only aluminum
substrate then cured at 340.degree. F. (171.degree. C.) for 20 minutes,
and tested as described above for filiform corrosion resistance, haze
rating, haze cracking, stability, thermal shock and 20.degree. gloss. The
following Table 3 illustrates the improvement in filiform corrosion
resistance, while maintaining other performance properties, obtained by
the incorporation of the particular carboxylic acid functional polyesters
of Example 1 and Example 2 into the powder coating composition.
TABLE 3
______________________________________
Test Example Example Example Example C-4
Performed: C-1 C-2 C-3 (comparative)
______________________________________
20.degree. Gloss
129 126 124 134
Haze rating 458 457 402 472
Haze Pass Pass Fail Pass
cracking
Stability 7 days, 7 days, 7 days, 7 days,
@35.degree. C. excellent excellent excellent excellent
Thermal Pass Pass Fail, slight Fail, slight
shock edge lift edge lift
Filiform 1 mm., low 5 mm., low 8 mm., high 10 mm., high
corrosion density density density density
______________________________________
Example D
This example describes the preparation of two powder coating compositions
based on an epoxy functional group containing acrylic polymer and a
carboxylic acid functional curing agent. Example D-1contains both the
carboxylic acid functional polyester of Example 1 and a carboxylic acid
functional curing agent, while Comparative Example D-2 contains only the
carboxylic acid functional polyester with no acid functional curing agent.
The powder coating compositions were prepared from a mixture of the
following ingredients:
______________________________________
Comparative
Example D-1 Example D-2
Ingredients: (grams) (grams)
______________________________________
Polyester of Example 1
70.6 70.6
Dodecanedioic acid 103.0 --
GMA acrylic resin.sup.1 414.4 414.4
EPON 1001F 35.4 35.4
URAFLOW B 4.4 4.4
TINUVIN 900 3.7 3.7
TROY 570 3.7 3.7
______________________________________
.sup.1 ALMATEX A207S available from Reichold Chemicals, Inc.
The ingredients of each of the Examples D-1 and D-2 immediately above were
mixed via typical powder compounding techniques. Each powder composition
was electrostatically applied to cleaned only aluminum substrate then
cured at 340.degree. F. (171.degree. C.) for 20 minutes, and tested as
described above for appearance (rated by visual inspection), haze rating,
20.degree. gloss, and extent of cure. The following Table 4 illustrates
that the carboxylic acid functional polyester is present in the powder
coating compositions of the invention in an amount insufficient to cure
the coating composition in the absence of the curing agent.
TABLE 4
______________________________________
Test performed:
Example D-1
Example D-2
______________________________________
Appearance smooth, clear
smooth, clear
MBK solvent rubs (200.times.) Pass, slight Fail at 100 rubs, complete
scratch break through
20.degree. Gloss 128 128
Haze rating 457 456
______________________________________
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